https://developer.mozilla.org/en-US/docs/Web/API/FontFaceSet/add
FontFaceSet: add() method - Web APIs | MDN
The add() method of the FontFaceSet interface adds a new font to the set.
web apisaddmethodmdn
https://developer.mozilla.org/en-US/docs/Web/API/FontFaceSet/load
FontFaceSet: load() method - Web APIs | MDN
The load() method of the FontFaceSet forces all the fonts given in parameters to be loaded.
web apisloadmethodmdn
https://lists.w3.org/Archives/Public/public-css-archive/2018Jun/0086.html
Re: [csswg-drafts] [font-loading] FontFaceSet.ready never resolves if no font faces are requested...
https://developer.mozilla.org/en-US/docs/Web/API/FontFaceSet/loadingerror_event
FontFaceSet: loadingerror event - Web APIs | MDN
The loadingerror event fires when fonts have finished loading, but some or all fonts have failed to load.
event webapismdn
https://developer.mozilla.org/en-US/docs/Web/API/FontFaceSet/ready
FontFaceSet: ready property - Web APIs | MDN
The ready read-only property of the FontFaceSet interface returns a Promise that resolves to the given FontFaceSet.
ready propertyweb apismdn